1. Field of the Invention
This invention relates to a modulation method, a modulation apparatus, a demodulation method, a demodulation apparatus, a recording medium, a transmission apparatus, and a transmission method. In addition, this invention relates to a method of recording auxiliary information, an apparatus for recording auxiliary information, a method of reproducing auxiliary information, an apparatus for reproducing auxiliary information, a method of reproducing data, and an apparatus for reproducing data.
2. Description of the Related Art
EFM (eight to fourteen modulation or 8–14 modulation) is used for digital signals recorded on CDs (compact discs). EFM converts every 8-bit block of an input digital signal into a 14-bit code word, and adds 3 margin bits to the 14-bit code word to form a 17-bit block of an output bit stream (a modulation-resultant bit stream). The used 14-bit code words are chosen to follow run length limiting rules “RLL(2, 10)” such that 2 to 10 successive bits of “0” should be between bits of “1”. Also, the added margin bits are chosen so that portions of the modulation-resultant bit stream between the 14-bit code words will follow the run length limiting rules “RLL(2, 10)”. The run length limiting rules “RLL(2, 10)” reduce DC and low-frequency components of the modulation-resultant bit stream.
EFM+ (8–16 modulation) is used for digital signals recorded on DVDs (digital versatile discs). EFM+ converts every 8-bit block of an input digital signal into a 16-bit code word forming a 16-bit block of an output bit stream (a modulation-resultant bit stream). The used 16-bit code words are chosen to follow the run length limiting rules “RLL(2, 10)”. Also, the used 16-bit code words are designed to enable the combination of the 16-bit code words, that is, the modulation-resultant bit stream, to follow the run length limiting rules “RLL(2, 10)”.
Japanese patent application publication number P2000-286709A discloses a modulation system which includes a formatter, an 8–15 modulator, and an NRZI converter. The formatter converts an input digital signal into a second digital signal of a predetermined format. The formatter outputs the second digital signal to the 8–15 modulator. The 8–15 modulator contains a set of 7 different encoding tables. The 8–15 modulator converts or encodes every 8-bit block of the output digital signal from the formatter into a 15-bit code word by referring to the set of the encoding tables. The 15-bit code word forms a 15-bit block of a modulation-resultant bit stream (a modulation-resultant digital signal). The 15-bit code word is chosen to enable its NRZI conversion result to follow run length limiting rules such that a minimum run length is 3T and a maximum run length is 11T where T denotes the length or period of one bit (one channel bit). The 8–15 modulator outputs the modulation-resultant bit stream (the modulation-resultant digital signal) to the NRZI converter. The NRZI converter subjects the output digital signal of the 8–15 modulator to NRZI modulation, thereby generating a digital signal of an NRZI code.
In the modulation system of Japanese application P2000-5286709A, each of the encoding tables stores 15-bit code words assigned to different states of an input 8-bit block. In addition, each of the encoding tables contains state information for selecting one from the encoding tables which will be used to convert a next input 8-bit block. This design is to enable the NRZI conversion result of a succession of two 15-bit code words to follow the run length limiting rules. The contents of the encoding tables are optimized in view of information about the frequencies of occurrence of different states of an input 8-bit block. Furthermore, first and second specified ones of the encoding tables are designed so that the NRZI modulation results of 15-bit code words in the first specified encoding table which correspond to prescribed input 8-bit blocks will be opposite in polarity (“odd-even” in the number of “1”) to those of 15-bit code words in the second specified encoding table.
In the modulation system of Japanese application P2000-286709A, since there is a plurality of the encoding tables, two candidate 15-bit code words may be selected in response to one input 8-bit block. DSVs (digital sum variations) are calculated for the candidate 15-bit code words, respectively. The absolute values of the DSVs are compared. One of the candidate 15-bit code words which corresponds to the smaller of the absolute values of the DSVs is finally selected as an output 15-bit code word. In this way, DSV control is implemented.
Japanese patent application publication number 10-269289/1998 discloses a digital contents distribution managing system in which a distributor side encrypts and compresses original digital contents information into encryption-resultant contents information. The distributor side transmits the encryption-resultant contents information, encryption-resultant key information, and encryption-resultant accounting information to a communication opposite party, that is, a user side. The distributor side receives contents-use information from the user side. The distributor side implements a process of collecting a charge for using the original contents information on the basis of the received contents-use information. The distributor side also implements a process of dividing the collected charge among the parties concerned which include the holder of the copyright of the original contents information. The user side decrypts the encryption-resultant key information to recover the original key information. The user side decrypts the encryption-resultant contents information in response to the recovered original key information, and expands the decryption-resultant contents information into the original contents information. The user side decrypts the encryption-resultant accounting information to recover the original accounting information. The user side updates the original accounting information in accordance with use of the original contents information. The user side transmits the related contents-use information to the distributor side. The user side can install the original contents information on a portable storage medium or a removable storage medium.
Japanese patent application publication number 10-283268/1998 discloses a recording medium which stores an encrypted version of main information and an encrypted version of key information. The key information can be used in decrypting the encrypted version of the main information. The encrypted version of the key information has a non-encrypted portion containing control information. The control information represents conditions for permitting the decryption of the encrypted version of the main information. The control information has machine information and region information. The control information prevents a user side from copying the encrypted version of the main information onto a hard disk or an optical disk.
In general, the inner portion of the disc member of each DVD is formed with a burst cutting area (BCA) for copy protection.
Japanese patent application publication number 11-120633/1999 discloses an optical disc having watermarks which are visible from the reproducing surface side of the disc, and which can be hardly formed on a forged disc. The optical disc includes a main transparent substrate on which a reflection layer, an adhesive layer, and a dummy transparent substrate are successively laminated. The adhesive layer is made of adhesive agent whose curing rate depends on the rate of the exposure to electromagnetic radiations. The reflection layer and the adhesive layer are located between an information-signal recording surface of the main transparent substrate and a first surface of the dummy transparent substrate. During the fabrication of the optical disc, a mask with a pattern for making the watermarks is placed above a second surface of the dummy transparent substrate which is remote from the adhesive layer. Electromagnetic radiations are applied via the mask to the adhesive layer. The curing rate of the adhesive agent spatially varies in accordance with a pattern of the mask so that a distribution of stresses which depends on the pattern of the mask occurs on the reflection layer. As a result, the reflection layer slightly deforms in accordance with the pattern of the mask. The deformation of the reflection layer forms the watermarks. Such watermarks enables legitimate discs and forged discs to be discriminated from each other.